A short range communication system called DSRC (Dedicated Short Range Communication) is known. DSRC is a wireless communication system for radio wave ranges of between several meters and several tens of meters used in ETC (Electronic Toll Collection Systems) and ITS (Intelligent Transport Systems). ETC is a system for paying tolls automatically which works by conducting communication between an antenna disposed on a tollgate and an in-vehicle device installed in a vehicle when an automobile passes through a toll booth on an expressway or the like. Using ETC eliminates the need to stop at toll booths, and hence the amount of time required for the automobile to pass through the tollgate is reduced greatly. As a result, traffic congestion in the vicinity of toll booths can be eased, and exhaust gas amounts can be reduced.
ITS is a transport system fusing a system for providing automobiles with intelligence such as a car navigation system, and a system for providing roads with intelligence such as a wide range traffic control system. Examples of a car navigation system include a system enabling collaboration with VICS (Vehicle Information and Communication Systems) When ITS is used in this way, information relating to minor roads gathered by the police and information relating to expressways gathered by the Metropolitan Expressway Public Corporation and the Japan Highway Public Corporation is edited and issued from the VICS center. Upon reception of this information, the car navigation system is able to search for a route which bypasses a traffic jam or the like, and display the route on its monitor.
Typically, a patch antenna is used as the antenna in DSRC and ETC. A constitutional example of a prior art patch antenna is shown in FIG. 21.
In the prior art patch antenna 100 shown in FIG. 21, an antenna substrate 103 is provided on a ground plate 101 via a spacer 102. A patch element 103a is formed on the antenna substrate 103 as a rectangular patch. Perturbation elements are formed at the apexes of the opposing angles of the patch element 103a, thus forming a circularly polarized wave antenna. The patch antenna is assembled by screwing screws into screw holes 106 provided in the four corners such that the ground plate 101, spacer 102, and antenna substrate 103 are integrated. A cable 104 for feeding the patch element 103a is led out from the rear surface of the antenna substrate 103, and a connector 105 is provided on the tip end thereof. The connector 105 is connected to a communication device having a reception function.
However, the required constitutional components of the patch antenna 100 shown in FIG. 21 are the ground plate 101, the spacer 102, the antenna substrate 103, double-sided tape to adhere the spacer 102 to the groundplate 101, and double-sided tape to adhere the antenna substrate 103 to the spacer 102. Furthermore, the patch antenna is assembled by screwing screws into the screw holes 106 provided in the four corners. The large number of required components and the complexity of assembly are problems. Moreover, the patch element 103a must be formed on the antenna substrate 103 by deposition or the like, and hence the construction of the antenna substrate 103 formed with the patch element 103a is both time-consuming and expensive.
It is therefore an object of the present invention to provide a patch antenna which is reasonably priced and easy to assemble.